Modern humans (left) have brains that are more than three times larger than our closest living relatives, chimpanzees (right) [Image: Aida Gomez-Robles, University College London. Original skull image from FineArtAmerica ]

Modern humans have brains that are more than three times larger than
our closest living relatives, chimpanzees and bonobos. Scientists don’t
agree on when and how this dramatic increase took place, but new
analysis of 94 hominin fossils shows that average brain size increased
gradually and consistently over the past three million years.

The research, published this week in The Proceedings of the Royal Society B,
shows that the trend was caused primarily by evolution of larger brains
within populations of individual species, but the introduction of new,
larger-brained species and extinction of smaller-brained ones also
played a part...